1. Field of the Invention
The present invention relates to phase-change information recording medium (hereafter, may be referred to as “phase-change optical information recording medium”, “optical recording medium”, “optical information recording medium” or “information recording medium”) which can perform at least one of recording, reproducing, erasing or rewriting of information by an optical change in the material forming a recording layer induced by laser beam irradiation, manufacturing method for the phase-change information recording medium, sputtering target, method for using the phase-change information recording medium and optical recording apparatus.
2. Description of the Related Art
Presently, a recording layer material of DVD (Digital Versatile Disk) system which can perform a speed recording at 2.5 double speeds (about 8.5 m/s) has been developed and the demand for more high-speed recording is increasing. For this reason, materials for various phase-change recording layer are being investigated. For example, AgInSbTe material (Japanese Patent Application Laid-Open (JP-A) No. 2000-339751 for reference), GeGaSbTe material (JP-A No. 2002-225437 for reference), GeInSbTe material (JP-A No. 2002-264515 for reference), InSbSn material (JP-A Nos. 09-286174 and 09-286175 for reference), and the like have been proposed.
Among these materials for phase-change recording layer used for DVD+RW(Digital Versatile Disc-Rewritable), there is a AgInSbTe material conventionally used for CD-RW which has been reformed to be capable of recording and erasing at high linear velocity. Since this AgInSbTe material corresponds to recording speed of high linear velocity region, a material in which the content of Sb is adjusted to be larger than that of recording material for CD-RW is being used. However, materials of high Sb composition ratio have a problem of lowering the crystallization temperature even though the crystallization speed increases. It is known that a decrease in crystallization temperature causes storage reliability deterioration. This problem of storage reliability of the phase-change information recording medium has been controlled by increasing Ag in the recording material of phase-change recording layer or by adding a quintessence such as Ge to keep it in an acceptable level from a practical standpoint up to 4-double speed DVD medium. However, an increase in the content of Sb for achieving higher linear velocity recording causes rapid decrease in crystallization temperature resulting in an extreme deterioration of amorphous mark stability. For this reason, it is assumed that the limit for making high-speed recording medium utilizing AgInSbTe material fit for practical use is as high as 4-double speed DVD.
On the other hand, GaSb material for high-speed recording material of 4-double speed or more is being investigated. The GaSb material can perform a high-speed recording and at the same time, excels in storage reliability. However, GaSb material has low recording sensitivity because of high melting point of 600° C. and has a drawback of requiring high power for high-speed recording. In addition, the crystallization speed must be accelerated by increasing the content of Sb in order to pursue a speeding up with GaSb material. However, when the content of Sb is 90 atomic percent or more, Sb becomes phase-separated and cannot pursue a uniform initial crystallization. If a uniform initial crystallization cannot be completed, initial recording property from the first recording to about 10 repeated recordings is notably deteriorated and cannot be put to practical use.
Hence, a phase-change optical information recording medium which is easy to perform initial crystallization, exhibits good recording sensitivity at a linear velocity as high as 10 double speeds or more with as much capacity as DVD-ROM, is capable of repeated recording and has excellent storage reliability, and its associated technologies have not yet been provided, and their soon provision is desired under current circumstances.